1. Field of the Invention
The present invention relates to a pressure release mechanism for a heating apparatus using saturated vapor as a heating medium, which will be widely used for manufacturing and forming synthetic resin products and others.
2. Description of the Prior Art
Heretofore this type of pressure release mechanism has been provided as shown in FIGS. 10 and 11 by way of example. In FIG. 10 a heating apparatus 71 in which saturated vapor is used as a heating medium includes a heating chamber 72, a heating medium in liquid 73 suitably selected depending on required heating temperature and accommodated therein, an electric heating device 74, saturated vapor 75, a heating zone 76 in which an object is placed to be heated, and a pressure release mechanism 77.
A pressure release mechanism for such heating apparatus is constructed as shown in FIG. 11 by way of example, which includes flanges 78, and pipes 79 connected therewith by welding 80. The flanges are fixed with each other by bolts served as fastening means 81. The mechanism further includes a rupture plate 83 which is made of metal such as aluminum, silver, Inconel, stainless, etc. and is placed in air tight condition by use of packing such as an O-seal ring made of Teflon, metal, etc.
When the pressure within said heating chamber 72 in FIG. 10 increases to a predetermined level, the rupture plate 83 will break and split open to release the internal saturated vapor out of the heating chamber 72 so as to prevent an excessive increase of the internal pressure.
Such known mechanism, however, has a drawback in that while in operation, the heating chamber 72 keeps the internal pressure at a level higher than the atmospheric pressure, the internal pressure decreases down to a level below the atmospheric pressure when the power 85 is turned off and the apparatus is left out of service, and with a lapse of time a slight volume of the air intrudes in the heating chamber 72 via the seal ring 84 due to unknown reasons. Even the use of a modified seal ring made of Teflon or metal has failed to achieve strict protection from the air intrusion causing such intrusion in a long, for instance 10 days of, suspension of operation.
Such intruded air deteriorates heat transmission capacity of the heating chamber 72 and needs to be forced out of the chamber before the apparatus is restarted, and the apparatus needs to be kept out of operation during the procedure. The apparatus is also provided with a branch pipe, not shown, having a valve and disposed on the pipe 79 located upstream of the pressure release mechanism 77 in order to exhaust the intruded air. The branch pipe is closed by the valve after use.